PEMBROKE, N.H. -- Potentially harmful levels of naturally occurring arsenic, uranium, radium, radon and manganese have been found in some bedrock groundwater that supplies drinking water wells in New England, according to a new U.S. Geological Survey study.

While the presence of contaminants, such as arsenic, in some groundwater was already known, this new study identifies several that hadn’t been previously identified. This new report also provides information on the type of bedrock geologic formations where high concentrations are most likely to be found, which will help identify areas most at risk of contamination.

The results highlight the importance of private well owners testing and potentially treating their water. While public water supplies are treated to ensure that water reaching the tap of households meets federal requirements, there are no such requirements for private supplies, which serve more than 2.3 million people in the region. Private well owners can find information on how to have their wells tested here. All of the contaminants identified can be reduced or eliminated through a variety of treatments.

"The same geologic forces which gave rise to the spectacular mountains and architecturally significant rock quarries of New England are also responsible, over time, for leaching trace contaminants into the groundwater that can be harmful to human health," said USGS Director Marcia McNutt. "This study helps focus attention on where and what the risk factors are such that citizens who depend on private wells can get their water tested to ensure peace of mind."

Among the findings, arsenic in untreated samples exceeded federal safety standards for public drinking water at 13 percent of sites – nearly double the national rate. Manganese exceeded its human-health benchmark in more than 7 percent of wells tested. Radon exceeded the U.S. Environmental Protection Agency’s proposed standards in 33 percent of wells. Additionally, uranium, which is easily measurable, was found to be a significant predictor of the presence of other forms of radioactivity (radon, radium, gross alpha radioactivity) that are a cause of concern for human health.

The study, part of an ongoing national effort by the USGS to systematically assess the quality of the Nation’s most important aquifers, is the most comprehensive study of the quality of New England’s bedrock groundwater to date.

“The concentrations above human health benchmarks and the wide variety of natural and man-made contaminants found show the vulnerability of crystalline rock aquifers that millions of people rely on to produce safe drinking water,” said USGS scientist and lead author Sarah Flanagan. “The well-to-well variability of water quality from bedrock aquifers in the region underscores the importance of testing public and private wells individually.”

"The bedrock aquifer in New England is a crucial drinking water resource, supplying water for the majority of our 2.3 million private well owners and many small public water systems in the region," said Curt Spalding, regional administrator of the U.S. Environmental Protection Agency's New England office. "This and other scientific studies on bedrock groundwater quality conducted by the USGS provide the scientific foundation for implementing protection programs to ensure that all New Englanders have access to safe, clean drinking water."

For this study, scientists examined water-quality data from more than 4,700 public-supply wells that were sampled for the USEPA Safe Drinking Water Program from 1997 to 2007 and 117 private wells sampled by the USGS National Water-Quality Assessment Program from 1995 to 2007. The samples included only well water from crystalline rock aquifers found in most of New England and small portions of northern New Jersey and southern New York State.

Depending on concentrations and the period of time someone consumes the water, among the potential health issues associated with drinking water containing these contaminants at levels above human health benchmarks include various types of cancer; reproductive and developmental problems; kidney and blood diseases; diabetes; and a weakened immune system.

“This study confirmed many areas already known to have groundwater with high levels of arsenic and radiochemicals and revealed for the first time, the potential fluoride hotspots in parts of the White Mountain region of northern New Hampshire,” said Flanagan.

These hotspots are locations with naturally occurring fluoride that can exceed drinking water standards.

“We also found that high concentrations of many naturally occurring compounds in groundwater were related to specific bedrock formations,” added Flanagan.

In addition to natural sources, human activities affected the quality of groundwater from New England’s crystalline rock aquifers. The researchers found sodium and chloride in water sources, both naturally occurring as well as that from road salt; nitrates; MtBE (methyl tert-butyl ether) and chloroform; and, rarely, pesticides. The concentrations of these contaminants were all below levels of human health concern, but some, such as chloride, had the potential to impact aquatic organisms.

The complete results of the study, Quality of Water from Crystalline Rock Aquifers in New England, New Jersey, and New York, 1995-2007, by Sarah M. Flanagan, Joseph D. Ayotte, and Gilpin R. Robinson, Jr., are available online.

Private well owners in New England can contact their State Drinking Water Programs for guidance and information about well maintenance, testing, and in-home water treatment options.